The invention relates generally to prosthetic components used in joint arthroplasty, and more particularly to an acetabular cup having enhanced fixation properties within the acetabulum of a patient.
Joint arthroplasty is a well known surgical procedure by which a diseased and/or damaged natural joint is replaced by a prosthetic joint. Joint arthroplasty is commonly performed for hips, knees, elbows, and other joints. The health and condition of the joint to be replaced dictate the type of prosthesis necessary to replace the natural joint. For example, in a total hip arthroplasty an acetabular cup is implanted in the acetabular cavity in the pelvis to replace the natural acetabulum. Replacement of the acetabulum is necessary when there is an inadequate articulation surface for a head or ball of a prosthetic femoral component.
To implant an acetabular cup, a cavity is reamed in the acetabulum. The reamed cavity generally conforms to an outer surface of the acetabular cup. The acetabular cup is then inserted into the formed cavity and secured by mechanical means, interference fit, or by a combination thereof. The acetabular cup is positioned in the pelvis at a fixed orientation with respect to patient anatomy and should remain stable.
Movement of the implanted acetabular cup over time can erode the surrounding bone of the acetabular cavity. The effect of such bone erosion is the loosening of the acetabular cup, allowing it to shift in position. Positional displacement of the acetabular cup with respect to the acetabulum can lead to dislocation of the joint.
Acetabular cup displacement can also generate excessive wear debris in which particulate material, which can interfere with joint articulation, is present within the joint. As the acetabular cup moves with respect to the pelvis, the implanted femoral head may no longer articulate in the acetabular cup within a desired range of motion. Improper positioning of the femoral head with respect to the acetabular cup can also accelerate the generation of wear debris creating a need for revision surgery.
Revision procedures in which the acetabular cup is replaced with a new prosthesis pose challenges as the replacement acetabular cup must be securely implanted in the pelvis. Bone erosion that typically necessitates such a revision procedure often produces an acetabular cavity having an elongated shape that does not provide the most favorable conditions for an interference fit with many acetabular cups. Although bone grafts can be effected to reshape the acetabular cavity to be generally hemispherical, there are certain drawbacks to such bone grafts. For example, a suitable graft bone may not be readily available, it may be difficult to secure the bone graft to the existing bone, and the graft material may not provide sufficient mechanical strength.
Various methods and techniques are presently used to secure an acetabular cup in a cavity formed in the acetabulum of a patient. One such method includes the use of bone cement to secure the acetabular cup to the acetabulum. Another technique utilizes an acetabular cup having holes for receiving screws, or other such fasteners, to affix the acetabular cup to bone.
Acetabular cups with a variety of external geometries are known in the art. For example, U.S. Pat. No. 5,571,201 (Averill et al.) discloses an acetabular cup having a plurality of unidirectional steps for engaging bone. U.S. Pat. No. 5,358,532 (Evans et al.) discloses an acetabular cup having a plurality of parallel annular rings disposed about an outer surface of the acetabular cup. The rings extend from a rim portion of the cup in a direction towards the apex of the cup. U.S. Pat. Nos. 4,662,891 (Noiles) and 5,413,603 (Noiles et al.) also disclose acetabular cups with stepped outer surfaces.
Although, such acetabular cups are able to achieve some degree of fixation to the acetabulum of a patient, an acetabular cup is desired that more effectively remains affixed in the acetabular cavity to reduce the likelihood of joint dislocation, minimize wear debris, and avoid revision surgery.